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Thread: Garbled screen and 486 won't boot

  1. #1
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    Default Garbled screen and 486 won't boot

    Just put together a computer with a 133mhz AMD 5x86 but I'm getting some very odd behavior with it. Sometimes it won't post, sometimes it freezes while detecting hard drives or when trying to boot, sometimes the screen is just a garbled mess. Just very inconsistent. So far I ruled out the cpu, ram, any of the drives and the video card. I'm thinking the issue is the motherboard. Maybe a bad bios?

  2. #2
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    Quote Originally Posted by RadRacer203 View Post
    Just put together a computer with a 133mhz AMD 5x86 but I'm getting some very odd behavior with it. Sometimes it won't post, sometimes it freezes while detecting hard drives or when trying to boot, sometimes the screen is just a garbled mess. Just very inconsistent. So far I ruled out the cpu, ram, any of the drives and the video card. I'm thinking the issue is the motherboard. Maybe a bad bios?
    Check the PS or swap it out with a known good one.
    Surely not everyone was Kung-fu fighting

  3. #3
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    For the motherboard, what is the make and model of said board? Check for bad traces and solder joints (cold or cracked) and reflow as necessary.
    Current retro systems:
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  4. #4
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    Well, I guess I didn't do a very thorough job of narrowing it down last night. This morning I was doing some testing and accidentally left the cache stick out and it worked just fine. Pulling my hair out trying to figure it out and it was the cache the whole time. I guess I need a new stick then. How rare is M919?

  5. #5
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    The motherboard? I see one on eBay. Does the board use a Cache on a Stick (COAST) Module?
    Current retro systems:
    2x Commodore 64 Breadbin 250407 Rev. B and C
    Packard Bell Pack-Mate 28 Plus, aka, the Ultimate Sound Card machine
    iMac G3/600 Graphite, Mac OS X 10.4.11 Tiger, Lubuntu 16.04.3 LTS
    iMac G4/800 Lampshade, Mac OS X 10.4.11 Tiger
    YouTube channel: https://www.youtube.com/c/RetroPCUser

  6. #6
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    Yeah, the cache on a stick is 256k and is labelled M919

  7. #7
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    You have a PC-CHIPS M919, it was a horrible Taiwanese clone board that was literally made entirely out of counterfeit parts. The chipset was an illegal reverse engineered clone by UMC, and the cache chips to the right of the RAM slots are fake. They're literally just molded plastic with pins stuck around the sides. The original BIOS on the board was a pirated Award BIOS with numerous bugs and stability issues. There is an updated BIOS available, but it requires a flashable BIOS chip.

    http://th2chips.freeservers.com/m919/

    Along with the fake cache chips on the board, the cache slot is also fake. Despite it looking like a COAST slot that was used on later Pentium era motherboards, it is most definitely not. DO NOT plug a COAST module into the slot, you risk burning the module and destroying the board. If there is something in the slot, remove it immediately.

    There is a special proprietary cache module that goes with this board. I've never seen one, but they apparently do exist. As to whether they actually work or not is unknown since the BIOS is programmed to fake 256k of cache.

  8. #8
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    Wow, I would have never guessed that's what I have. Kind of cool to have such a bad knockoff, but it honestly works pretty well apart from the cache going bad. I got the board for free so even without cache I'm fairly pleased with it

  9. #9

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    PC Chips was notorious for these kind of shenanigans. See my post regarding the PC Chips M590 with the 100mhz bus that wasn't:

    http://www.vcfed.org/forum/showthrea...953#post554953

  10. #10
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    Quote Originally Posted by RadRacer203 View Post
    Wow, I would have never guessed that's what I have. Kind of cool to have such a bad knockoff, but it honestly works pretty well apart from the cache going bad. I got the board for free so even without cache I'm fairly pleased with it
    I used to have one of those boards with no cache on it and it worked fine after I updated the BIOS. I had an AMD 5x86-133 @ 160 in it with 192 MB of RAM. I unfortunately got rid of it a number of years ago in a PC parts purge. I should have kept it, but the case was crappy and damaged and I didn't have the money to get another at the time.

    I have one 486 machine now, but it's nowhere near as good despite being in much better condition. The max CPU speed is 66 MHz, and while it does accept an overdrive CPU, it only runs it at 33 MHz due to a BIOS bug. I also have a lose Zeos 486 motherboard, but it only works with Intel chips.

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